First day of spring today, but what does that mean?

Credit: Lisa Powell

Credit: Lisa Powell

Saturday, March 20 is the first day of spring this year – but what does that mean?

Today is actually the astronomical start of a season, which is determined by the summer solstice, winter solstice, fall equinox and spring equinox and is based on how the sun’s light hits the Earth at different times of the year.

For example, during the summer solstice, which happens around June 21 in the northern hemisphere, the Earth is tilted toward the sun, causing the longest day of the year.

The winter solstice, by contrast, is around Dec. 22 when the Earth is tilted away from the sun, causing the shortest day of the year.

Equinoxes come in between the solstices, when the Earth isn’t tilted at all relative to the sun, making day and night approximately the same length.

The vernal, or spring equinox comes around March 21, while the autumn equinox comes around Sept. 22.

The National Centers for Environmental Information said that meteorologists define astronomical seasons differently, however. Instead, meteorologists break the seasons down into groups of three months.

So, in the northern hemisphere, spring includes March, April and May; summer includes June, July and August; fall includes September, October and November; and winter includes December, January and February.

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